Introduction to the Messel Pit
Jack Wilkin (UK)
The Messel Pit represents a Konservat-Lagersttätte dating to the Eocene Epoch 47 million years ago. The site is in Hessen State in Germany, close to the city of Darmstadt. It is a disused oil shale quarry that was scheduled to become a landfill in the mid-1990s. Thankfully, due to public and scientific outcry, the site was designated as a UNESCO World Heritage Site in 1995. Ever since, there have been thousands of amazing and revolutionary discoveries. This article seeks to introduce this remarkable site and a glimpse into a lost world.
During the Eocene, global temperatures were much higher than they are today. The area that is now Messel was a volcanic lake surrounded by subtropical rainforests. The upper portions of the lake supported a wide diversity of organisms. The bottom waters where anoxic. This prevented bioturbation and inhibited bacterial decay leading to exceptional preservation. The lake would have periodically released toxic gases, in much the same way as Lake Nyos in northwest Cameroon, did in 1987 to lethal effect. The pit is comprised of oil shales. The rocks have a high-water content and any fossils recovered must be kept moist or else they will dry out and the specimen will be lost forever. They must also be stabilised with resin, in a process called the “transfer technique”.
The Messel Pit is unusual in that both plant microfossils and macrofossils are founds found in abundance. The types of plants found at Messel are ones you would expect from mid-to-low latitudes today. By studying the morphology of fossil leaves, it is possible to make assumptions about the local climate. Messel plants had long leaves with ‘drip tips’ and large stomata (that is, microscopic pores found on the epidermis of plants), which are commonly associated with warm, humid environments. One such group of tropical plants was the genus Canarium, which today are found across equatorial Africa, Indochina, Australia and the Pacific Islands.
The most common fossils at Messel are those of insects, especially beetles. Not only are anatomical details preserved in exquisite detail, but colour patterns are also present. Jewel beetles (Buprestidae) are distinguished by their preserved colour structures that, even after 47 million years, still shimmer with their original iridescence. The largest insect from the Messel was the ant genus, Formicium, which had a wingspan of up to 16cm. This ant would have behaved in much the same way as modern army ants, devouring anything unlucky enough to get in its path.
Fish are the most common vertebrates from the Messel Pit (Fig. 1). The most abundant were the gars and bowfins, which comprised up to 90% of fish diversity from some layers. The gar, Atractosteus strausi, had a massively built skull, a protruding crocodile-like snout and thick enamel covered scales. Gars are primitive bony fish that today are restricted to rivers in the Americas, slowly ambushing their prey. To deal with the low oxygen conditions in the lake, many bowfins and gar processed swim bladders specially adapted to allow them to ‘breath’ the air directly. Specimens showing signs of reabsorption of minerals on scale margins as a response to vitamin deficiency are commonplace. A single eel, closely related to the catadromous eels (ones that are born in the sea but spend their lives in fresh water) has been discovered, suggesting that the Messel lake was connected to the sea by rivers. Most fishes from the Messel lake are juveniles that perished before reaching sexual maturity.
Amphibians are very rare at Messel, due in part to the inhospitable nature of the lake and the limited environmental tolerances of amphibians, with only five species known thus far. The most common amphibian was the terrestrial frog, Eopelobates (Fig. 2). This had long limbs and a powerfully built skull that preyed on small reptiles and even mammals. The preservation of these frogs in remarkable, with some showing skin and muscles. Semi-aquatic frogs are rare from the Messel lake, but tadpoles are also known.
After the end-Cretaceous extinction, reptile diversity has been in decline dropping from 20 Orders down to just four, with three (squamates, turtles and crocodilians) known from Messel. Squamates are represented by both lizards and snakes. Snakes first evolved during the Cretaceous and, by the Eocene, had developed into the recognisable forms we have today, including constrictors like the two-metre-long, extinct Paleophyon found at Messel. This spent a lot of its time in the water, as do its living relatives, and one specimen had the remains of a small crocodilian its stomach.
Crocodiles from Messel come in two forms: semiaquatic and terrestrial. The four-metre-long Asiatosuchus was the largest of the Messel crocodiles, which could ambush the largest Messel mammals. In contrast, Allognathosuchus was a heavily armoured species that had crushing, bulbous teeth designed to crush molluscs.
The largest of the Messel turtles was the 50cm, soft-shelled, fish-eating Trionyx. Specimens of the more common Allaeochelys (Fig. 3) – believed to be a transitional form between hard and soft-shelled turtles – are found as mating pairs, implying that their death was rapid. It is believed that they started copulating in the well-aerated surface waters, before sinking into the deeper toxic water, where they died.
Birds are the most common land vertebrates at Messel being represented by over 50 species (Fig. 4). The most abundant type was the Messelirrisoridae, a now extinct group, that perched in the trees surrounding the lake and occupied the ecological niche now filled by the songbirds (passerines). The most abundant bird is Messelornis (Fig. 5), the nicknamed the “Messel Rail”. The basal nightjar, Protocypselomorphus, had a short and wide beak, which would have functioned like an insect net.
An early relative of the ostriches was the peacock-sized, long-legged, Paleotis. The discovery of this species is of great paleogeographic interest, as living ratites are found only in the Southern Hemisphere, having drifted with respective continents during the break-up of Gondwana during the Cretaceous. The presence of ratites at Messel would strongly suggest that a land bridge existed connecting the former Gondwana to the then island continent of Europe. By far the most impressive and best known of the Messel birds was the two-meter tall, Gastornis. This behemoth was originally assumed to have been the apex predator. However, it is now known to have been a herbivore, using its powerful skull to crack open nuts. Colour pigments, called melanosomes, are preserved at Messel. By comparing fossilised melanosomes to those of modern birds, you can reconstruct the colour patterns of extinct birds.
Messel is best known for its mammals and is home to over 45 species. Bats are abundant and provide a unique insight into bat evolution. All belong to Microchiroptera, which are insectivorous forms and the remains of insects have been found in the stomach contents of many specimens. By the Eocene, bats had already diversified, with differences in wing biomechanics suggesting distinct species had different lifestyles.
The insectivore, Leptictidium (Fig. 6), belonged to a group of archaic placental called Proteutheria that lasted from the Cretaceous until the early Tertiary. It was about one metre long and had remarkably long hindlimbs, short forelimbs and an extremely long tail comprised of more than 40 vertebrae. This is all evidence of a jumping, bipedal locomotion. The otter-like Buxolestes was another Proteutheria that used its webbed feet and flattened tail to patrol the lake catching fishes.
Eomanis is the oldest known pangolin, a group currently restricted to the tropics of Africa and Southeast Asia, and has been found in Messel. Preserved gut contents show Eomanis ate both insects and plants, although its modern descendants only eat ants and termites. Pangolins use their powerful forelimbs to break into mounds and elongated sticky tongue to trap prey. Eomanis shares these features plus a few basal traits, such as a lack of scales on the tail and legs, implying a European origin for this group (see also Fig. 7).
The Messel Pit has some of the oldest known fossil horses. There are three genera present at this locality: Eurohippus, Propalaeotherium and Hallensia. Embryo remains have been found inside several specimens. Every pregnant mare carried only a single foetus, indicative of a high degree of parental care. Additionally, all the foetuses were at the same developmental stage, meaning that the mothers all died at the same time of the year.
Perhaps the most famous fossil is that of a basal lemur-like primate, Darwinius masillae, nicknamed ‘Ida’. Features such as grasping hands, nails rather than claws and forward-facing eyes all suggest an aboral lifestyle.
Further reading
Schaal, S (Editor). (2005) Messel Pit Fossil Site: Snapshots of the Eocene. Vernissage 21(5).
Selden, P., Nudds, J. (2012). Evolution of Fossil Ecosystems (2nd Ed.). Manson Publishing: London.
Tudge, C. (2009). The Link: Uncovering Our Earliest Ancestor. Little, Brown Book Group: London.